What's your water pressure? If it's overly high, that may be part of it. Without looking it up, Toto tends to use one of two fill valves, one is made by Korky for them, and the other (Vorato?). The Korky tends to be the quieter valve during shutoff.
If your tank is nice and vertical, you can continue to tighten the nuts to bring things into contact...check out the 'How to' instructions posted here. Basically, tighten maybe 1/2-1 turn, alternating from side to side. As long as you don't end up porcelain to porcelain, you should not be able to break it unless the tank is defective. Since I don't do it every day, I'll put a sheet of paper under each of the 'legs' and stop when I can still pull it out. This means you've only got a few thousandth's of gap, but do have a gap and there's no chance of trying to stretch the porcelain (which doesn't work!) and cracking something. You may find it easier after the gasket has been compressed - IOW, it may be easier to do it now after it's been sitting compressed for awhile, but it will snug down.